Garnet pyrope-grossular

Fig.1. Example broadband LIBS spectra for a pyrope, grossular, and spessartine garnet. The clear differences observed in the broadband spectra reflect the chemical differences in the composition of the three garnets.

Cressey G. (1978). Exsolution in almandine-pyrope-grossular garnet. Nature, 271 533-534. 

Ganguly J., Cheng W., and O Neill H. St. C. (1993). Syntheses, volume, and structural changes of garnets in the pyrope-grossular join Implications for stability and mixing properties. Amer Mineral, 78 583-593. 

Haselton H. T. and Newton R. C. (1980). Thermodynamics of pyrope-grossular garnets and their stabilities at high temperatures and pressures. J. Geophys. Res., 85 6973-6982. 

Hensen B. I, Schmid R., and Wood B. J. (1975). Activity-composition relationship for pyrope-grossular garnet. Contrib. Mineral Petrol, 54 161-166. 

Wood B. I (1988). Activity measurements and excess entropy-volume relationships for pyrope-grossular garnets. J. Geol, 96 721-729. 

Garnet Pyrope Mg3Al2(Si04)3 and Grossular Ca3Al2(Si04)3... 

Figure 47 Garnet compositions for eclogites from Siberia, South Africa, and Koidu (Sierra Leone) compared to low-L Kaapvaal peridotites, in terms of their pyrope, grossular, and almandine calculated end-members (sources Sobolev, 1974 Hatton and Gurney, 1987 Mazonne and Haggerty, 1989 Taylor and Neal, 1989 Jacob et al, 1994 Hills and Haggerty, 1989 Viljoen et al., 1996 Pyle and Haggerty, 1998 and Barth et al, 2001).

Now we have four elements mixing on two sites. This looks like a case of four components, pyrope, grossular, andradite and khoharite. However, any of these four formulas can be written as a linear combination of the other three (Spear, 1995, p. 184). We can therefore describe aU compositions of this garnet... 

The enthalpies of solution of several synthetic pyrope-grossular garnets were determined by Newton et al. (1977) by dissolving them in a liquid (2PbO-... 

Table 14.3 Enthalpies of solution of pyrope-grossular garnets at 970K. From Newton et al 1977, Table 3. Uncertainty is standard deviation from the mean. Number of calorimeter runs in parentheses. = soVnH - MeaisomH = (Equation 10.20).

Excess entropy of mixing has also been estimated from cryogenic or low-temperature calorimetry (Chapter 5) by Haselton and Westrum(1980). They determined - Sq at 298.15 K for pyrope, grossular, and a single intermdiate composition, Pyo.g Gto4. However, S2gs for the intermediate (Ca-Mg) garnet requires calculation of the residual entropy frozen in, i.e., the entropy of the crystal at 0 K. 

Figure 14.2 (a) Enthalpy of solution of synthetic pyrope-grossular garnets at 970 K. Data from Table 14.3. The solid line is calculated using a two-parameter Margules equation, (b) Measured and calculated from the same data set. 

Garnets (pyrope, almandine, spessartine, uvarovite, grossular, spessartine) Abrasives, blasting media, water jet cuttings, and water filtration. 

Garnet (pyrope, almamdine, spessartine, uvarovite, grossular, andradite) USA (101), India (100), Australia (100), and China 335,000 Almandine (8-250 mesh) 170-240... 

From the calculated activity coefficients a regular solution parameter for pyrope-grossular garnets is derived ... 

Fig. 3 Enthalpy of solution of pyrope-grossular garnets in a lead borate melt at 970 K (Newton et al, 1976). Dashed line is trend for ideal mixing dotted line is trend for regular solution with W = 3.82 kcal (Ganguly and Kennedy, 1974).

To make the important pressure correction to of the reaction, we must know the volume change of the reaction and its dependence on temperature. Using the volume data of Skinner and Boyd (1964) for aluminous orthopyroxene, of Clark et al (1962) and Warner and Luth (1974) for the clinopyroxenes, unpublished data of the author for pyrope-grossular garnets, and data for spinel and forsterite from Robie and Waldbaum (1968) we have Vq = 65.48 cm /gfw, Vqpx = 62.14, Vgp = 39.71, = H5.34 and%o = 43.78... 

Broadband LIBS spectra for three garnet types - the Mg-AI pyrope type, the Ca-AI grossular type, and the Mn-AI spessartine type are shown in Figure 1. 

Geiger C. A., Newton R. C. and Kleppa O. I (1987). Enthalpy of mixing of synthetic almandine-grossular and almandine-pyrope garnets from high-temperature solution calorimetry. Geochim. Cosmochim. Acta, 51 1755-1763. 

Direct observation of immiscibility in pyrope-almandine-grossular garnet. 

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